Thermo-elastoplastic modeling of UO2/Zr dispersion fuel

Dispersed fuel elements are widely utilized in research and test reactors. The high thermal conductivity of dispersion fuels allows a significant reduction of temperature in comparison to a standard oxide fuel. The main objective of this paper is a simulation of the displacement and the associated stresses using the governing equations for mechanical equilibrium, heat generation, heat transfer, stress–strain relationship, swelling, thermal expansion, fission-induced creep, created pressure by fission gas bubbles in a plate type cermet fuel, ${\mathrm{UO}}_2$ ceramic fuel in $\mathrm{Zr}$ as a metallic matrix, which is subjected to thermal and mechanical loadings. The mathematical derivations are obtained for an equivalent unit sphere cell containing an inner layer for fuel particles and an outer layer for matrix. The outcome stresses are verified against reference solutions. To implement the algorithm, a code-named Kowsar-2 is developed in which a fuel plate is discretized in the axial and through-thickness direction in the first step. Then the thermal calculation is carried out for each segment considering the effect of solid fission products, fission gases released over time along fission gas diffusion, bubble production, swelling, etc. Temperature of coolant, oxide layer, clad, and fuel are also obtained in this step. Mechanical treatments are followed for a typical cell to get stress and strain distributions.